1. Field of the Invention
The present invention relates to an apparatus for recording and/or reproducing information ion/from a recording medium and a method of accessing a recording and/or reproducing means in the apparatus to a desired track.
2. Related Background Art
Various conventional recording media such as disk-, card-, and tape-like media are known and used for recording or reproducing information with light. These optical information recording media include write/read type media and read-only media.
Information can be recorded in a recordable medium as follows. A modulated light beam spot is used to scan information tracks, and information is recorded as information bit arrays which can be optically detected.
Information can be reproduced from the recording medium as follows. A light beam spot having power which does not allow recording on the medium scans the information bit array of the desired information track, and light reflected by or transmitted through the medium is detected, thereby reproducing information.
A so-called optical head is used to emit the light beam spot on the recording medium described above and to detect light reflected by or transmitted through the recording medium. The optical head is moved relative to the recording medium in an information track direction or a direction perpendicular thereto. Relative movement of the optical head allows information track scanning with the light beam spot.
Of the conventional optical information recording media, a card-like optical information recording medium (to be referred to as an optical card hereinafter) is most promising because it can serve as a compact, lightweight, portable, large-capacity information recording medium. Apparatuses for recording/reproducing information in/from such an optical card are described in U.S. Pat. No. 4,787,075 and U.S. patent application Ser. No. 812,995 (filed on Dec. 24, 1985).
FIG. 1 is a plan view of an optical card which allows additional writing, and FIG. 2 is an enlarged view of its main part.
Referring to FIG. 1, a large number of information tracks 2 are formed on an information recording surface of an optical card 1 in the directed indicated by arrows L and F (the LP direction). A home position 3 is determined on the information recording surface of the optical card 1 and serves as a reference position for accessing the information tracks 2. The information tracks 2 are arranged in an order of 2-1, 2-2, 2-3,. . . from the home position 3. The information tracks include tracks in which information has already been recorded (to be referred to as recorded information tracks, hereinafter) and tracks in which information is not recorded (to be referred to as nonrecorded information tracks, hereinafter). Information can be recorded in the nonrecorded information tracks at any time.
As shown in FIG. 2, tracking tracks (e.g., 5-1, 5-2, and 5-3) are formed between the adjacent tracks 2 (e.g., 2-1 and 2-2). The tracking tracks are utilized as a guide for auto tracking (AT) so as to prevent a light beam spot in the recording and/or reproducing mode from deviating from a predetermined information track during scanning.
In the information recording or reproducing mode, the light beam spot is always located at the home position 3 and is accessed from this position to a target information track. This track access is performed by moving the optical head in a direction perpendicular to the information tracks and at the same time, moving some (e.g., an objective lens) of the optical elements in the optical head in the direction perpendicular to the information tracks. The latter operation is called a kick operation.
The kick operation is performed as follows. Pulses (kick pulses) are applied to an actuator to move the objective lens in the direction perpendicular to the information tracks after the AT control loop is opened. After a predetermined period of time has passed, pulses (brake pulses) having a polarity opposite to the kick pulse are applied to the actuator to brake the objective lens such that the speed of the light beam spot is zero when the spot reaches the information track adjacent to the target information track. This can be achieved by properly selecting the magnitudes and widths of the kick and brake pulses. At this time, the AT control loop is closed to guide the light beam spot to the target information track.
Whether the current track is the target information track or not is discriminated by the current information track number. As shown in FIG. 2, track number data are preformatted in an area 6 located on a line extending from the tracking tracks. The optical head is reciprocally moved relative to the optical head in the LF direction to read the number area. The position of the light beam spot can be detected on the basis of the read results. In another system, a track number is recorded in each information track every time information is recorded in the information track. The optical card is reciprocally moved relative to the optical head in the LF direction. The track number is extracted on the basis of the read result to detect the position of the light beam spot.
In the apparatus described above, the optical card is continuously moved in the LF direction to detect the track number, thereby accessing the target track. According to this method, however, the optical head cannot often be moved accurately to the target track by vibrations generated upon card driving. In addition, if a loading error of the optical card in the apparatus occurs, e.g., if an inclination (skew) of the track is present with respect to the moving direction of the optical card, the track positions are changed during access. Therefore, the final position of the light spot is undesirably deviated from the target track, and access time is prolonged.